The art is continually seeking new fluorocarbons which are useful as blowing agents. Fluorocarbons such as trichlorofluoromethane (known in the art as CFC-11 and which has a boiling point of 23.7.degree. C.) have been used commercially as auxiliary blowing agents for flexible foams and as primary blowing agents for rigid foams. Polyurethane foams are manufactured by reacting and foaming a mixture of ingredients comprising in general an organic isocyanate, such as pure or crude toluene diisocyanate or a polymeric diisocyanate, with an appropriate amount of polyol or mixture of polyols, in the presence of a volatile liquid blowing agent, which vaporizes during the reaction, causing the polymerizing mixture to foam. The reactivity of these ingredients is enhanced through the use of various additives such as amine and/or tin catalysts and surfactant materials which serve to control and adjust cell size as well as to stabilize the foam structure during its formation.
Flexible polyurethane foams are generally manufactured using an excess of diisocyanate which reacts with the water also included as a raw material, producing gaseous carbon dioxide, causing foam expansion. Flexible foams are widely used as cushioning materials in items such as furniture, bedding and automobiles. Auxiliary physical blowing agents such as methylene chloride and/or CFC-11 are required in addition to the water/diisocyanate blowing mechanism in order to produce low density, soft grades of flexible polyurethane foam.
Rigid polyurethane foams are almost exclusively expanded using CFC-11 as the blowing agent. Some rigid foam formulations do incorporate small amounts of water in addition to the CFC-11, but the CFC-11 is the major blowing agent component. Other formulations sometimes use small amounts of the more volatile dichlorodifluoromethane (known in the art as CFC-12 and which has a boiling point of -29.8.degree. C.) in addition to CFC-11 for producing so-called froth-type foams. Rigid foams are closed-cell foams in which the CFC-11 vapor is trapped in the matrix of cells. These foams offer excellent thermal insulation characteristics, due in part to the low vapor thermal conductivity of CFC-11, and are used widely in thermal insulation applications such as roofing systems, building panels, refrigerators and freezers and the like.
Currently, fluorocarbons are of particular interest because they are considered to be stratospherically safe substitutes for the presently used fully halogenated chlorofluorocarbons. The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer. CFC-11 and CFC-12 are controlled substances under the Montreal Protocol on Substances that Deplete the Ozone Layer. Mathematical models have substantiated that hydrochlorofluorocarbons are negligible contributors to ozone depletion and to green-house global warming in comparison to the fully halogenated species.
As discussed in "How to Fix the CFC Mix", CHEMICAL WEEK 64 (Oct. 18, 1989), alternative blowing agents for currently used CFC blowing agents include chlorodifluoromethane (known in the art as HCFC-22 and which has a boiling point of -40.8.degree. C.), 1,1-dichloro-2,2,2-trifluoroethane (known in the art as HCFC-123 and which has a boiling point of 27.8.degree. C.), 1-chloro-1,2,2,2-tetrafluoroethane (known in the art as HCFC-124 and which has a boiling point of -12.degree. C.), 1,1-dichloro-1-fluoroethane (known in the art as HCFC-141b and which has a boiling point of 32.degree. C.), and 1-chloro-1,1-difluoroethane (known in the art as HCFC-142b and which has a boiling point of -9.2.degree. C.).
The use of HCFC-123 as a blowing agent is disadvantageous because HCFC-123 has a high molecular weight; as a result, HCFC-123 is an inefficient blowing agent. The use of HCFC-141b or HCFC-142b as a blowing agent is disadvantageous because the vapors of HCFC-141b and HCFC-142b are flammable; as a result, the shipping, handling, and use of HCFC-141b and HCFC-142b have to be carefully controlled due to the potential flammability. The use of HCFC-22 and HCFC-124 as blowing agents is disadvantageous because they have such low boiling points.
U.S. Pat. No. 4,624,970 discloses the use of mixtures of CFC-11 and dichlorotrifluoroethane to blow urethane type foams. Such blowing agent mixtures were found to permit greater amounts of low cost aromatic polyester polyols to be used in rigid foam formulations without serious degradation in foam properties.
Although hydrochlorofluorocarbon blowing agents have low ozone depletion potentials compared with the fully halogenated chlorofluorocarbons, a need exists in the art for a method of preparing foam with a blowing agent which has a zero ozone depletion potential and is nonflammable.
It is an object of this invention to provide a method for the preparation of polyurethane and polyisocyanurate foams.
A further object of the invention is to provide environmentally acceptable blowing agents for the production of rigid and flexible polyurethane and polyisocyanurate foams.